Relief valves and the like have been employed in fluid operated systems to protect fluid operated motors and associated system componentry from excessive fluid pressure which is detrimental to the life of the motors and componentry. Typically the relief valves are connected to the system reservoir either directly or through a controlling valve of the system. In either situation a continuously open passageway between the relief valve and reservoir must be provided so that fluid flow from the relief valve to the reservoir may be freely passed.
Often the fluid operated system is utilized to controllably power an implement; such as provided on a lift truck or earthmover. In these applications, the use of a separate conduit to directly connect the relief valve to the reservoir is undesirable because, it reduces visibility past the implement, is subject to damage, and requires additional parts which adds to the cost and complexity of the vehicle.
In implements having a plurality of different functions, several fluid operated motors are normally provided. For example, a container handling attachment of a lift truck requires side shift, slew, extend, reach, and leveling functions. In such applications the jacks associated with each function must have the capability of being individually controlled. It has been found that the number of conduits connecting the conrolling valve to the jacks can be reduced to two when a selecting valve for each function is provided. The selecting valves are mounted on the implement and a single controlling valve for modulating fluid flow is mounted on the vehicle. The pair of conduits connect the controlling valve to the selecting valve and provide flow paths from a pump to the jack and from the motor to the reservoir. In this embodiment the selecting valves block flow between the controlling valve and the respective motors and thus isolate the jacks from the reservoir. Locating the relief valves between the selecting valves and the controlling valve prevents communication of the relief valves with the jacks, and locating the relief valves between the jacks and selecting valves isolates the relief valves from the reservoir. Providing a separate conduit to connect each relief valve to the reservoir is not a viable solution for substantially the same reasons as discussed above.
The present invention is directed to overcoming one or more of the problems as set forth above.